This invention relates to a photopolymerizable composition. More particularly, it relates to a photopolymerizable composition which is suited above all to a solder resist for preparation of a printed circuit board since it is capable of forming a cured coating film which is superior in adhesion to a substrate, thermal resistance and in resistance to chemicals and from which an uncured coating film can be removed simply on flushing with water. The present invention also relates to a method of forming a cured coating film pattern using the photopolymerizable composition.
Up to now, when soldering components to a printed board, a solder resist is applied to the surface of the printed board for avoiding adhesion of the solder to other than desired portions and for protecting the circuit on the printed board surface. The solder resist is applied in many cases by printing a resist composition as a desired pattern on the printed board such as by silk screen printing and subsequently by curing the printed pattern by heating or by active rays such as UV rays. Recently, with the tendency towards a higher density of the printed board, a liquid photoresist type solder resist having high pattern forming precision has been proposed. That is, a liquid photopolymerizable solder resist is applied by silk screen printing or roll coater printing on the printed board and dried on heating. A film having a desired pattern drawn thereon is tightly contacted with the coating film, and active rays, such as UV rays, is radiated for curing the exposed portion. An unexposed portion is removed by dissolution with a developing solution, and the cured portion is post-cured using heating or irradiation with active rays for forming a circuit protective film and a soldering pattern formed by the soldering resist.
With the above-mentioned conventional solder resist, an organic solvent is mainly employed as the developing solution. A developing solution employing an aqueous alkali solution in place of the organic solvent has also been developed. However, the solder resist employing the organic solvent as the developing solution presents problems such as conflagration or toxicity to a human body. On the other hand, the solder resist employing the aqueous alkali solution as the developing solution is inferior in properties of the resist film formed thereby to the solder resist of the heat curable type or of the type developed by the organic solvent.